1. Field of Invention
The present invention relates to an inkjet head for printing images/characters on a recording medium, and more particularly to an inkjet head including a common ink chamber for distributing ink to a plurality of ink pressure chambers.
2. Description of Related Art
FIG. 1 schematically shows a conventional ink flow channel formed in an inkjet head, which is disclosed in Japanese Patent Application Provisional Publication No. P2001-277496. The ink flow channel includes a plurality of ink pressure chambers 1020 connected to a common ink chamber 1026 through respective ink supply channels 1027. Ink to be ejected from the inkjet head is first introduced into the common ink chamber 1026 through an ink supply tube 1035 and then distributed therefrom to each ink pressure chamber 1020. The ink in each ink pressure chamber 1020 is selectively pressurized and thereby ejected from a nozzle 1013 which is in fluid communication with the pressure chamber 1020.
When pressure is repeatedly applied to the ink in one or more ink pressure chambers 1020, pressure waves transmit from the ink pressure chambers 1020 into the common ink chamber 1026 through the ink supply channels 1027. The pressure waves are partially reflected at closed ends 1026a of the common ink chamber 1026, such that the traveled pressure waves and the reflected pressure waves are superimposed. The superimposed pressure waves partially transmit through the ink supply channels 1027 to increase/decrease the pressure within the pressure chambers 1026. Such unintentional increase/decrease of the pressure within the pressure chambers 1026 causes increase/decrease of the amount of the ink ejected from the nozzles as well as breakage of the ink meniscuses formed in the nozzles. The breakage of the ink meniscuses may cause air to enter the nozzles and impair the functioning of the nozzles.
Therefore, there is a need for an inkjet head in which the pressure wave generated in one ink pressure chamber does not affect the ink in other ink pressure chambers (typically, adjacent) through the common ink chamber.
Japanese Patent Application Provisional Publication HEI 9-314832 also discloses an inkjet head provided with a plurality of ink pressure chambers and a common ink chamber connected thereto. The common ink chamber is formed to be U-shaped and is connected, at the middle thereof, to an ink supply channel. Ink from an external ink tank is supplied to the common ink chamber through the ink supply channel.
In the above mentioned inkjet head, pressure waves occur in the common ink chamber as the ink flows therein through the ink supply channel. The pressure waves transmit along the U-shaped common ink chamber toward the ends thereof. Then, the pressure waves are reflected at the ends of the common ink chamber and transmitted back along the common ink chamber to encounter pressure waves are subsequently generated and transmitted toward the ends of the common ink chamber. At locations of the reflected pressure waves and the subsequently generated pressure waves are encountered and superimposed on each other, such that a part of the pressure wave enters the ink pressure chambers, which increases/decreases the pressures of the ink pressure chambers, resulting in excessive/poor ink ejection from the corresponding nozzles.
It should be noted that the above mentioned inkjet head is further provided with a pair of narrow fluid channels extending from the ends of the common ink chamber. These fluid channels, however, are formed mainly to discharge air trapped in the common ink chamber and hence does not serve to effectively reduce the reflection of the pressure waves at the ends of the common ink chamber.
Japanese Patent Application Provisional Publication P2000-234170 discloses an inkjet head that includes a pair of common ink chambers for distributing ink among a plurality of ink pressure chambers. Each common ink chamber is formed in a relatively straight elongated shape and is connected to an ink supply channel at one end thereof so that ink from an external ink tank can be supplied thereto.
Japanese Patent Publication No. 2718010 also discloses an inkjet head that includes an elongated and substantially straight common ink chamber for distributing ink to a plurality of pressure chambers.
In the common ink chambers of the inkjet heads disclosed in the above mentioned two publications, the pressure waves are generated in the common ink channel, as ink is supplied thereto. The pressure waves transmit toward and are reflected back at the end of the common ink channel, and are superimposed on subsequently generated pressure waves which are similar to the pressure waves in the inkjet head disclosed in Japanese Patent Application Provisional Publication HEI 9-314832. Thus, the same problem, (i.e., insufficient/excessive ink supply) arises also in the inkjet jet heads disclosed in the above mentioned two publications.
Therefore, there is a need for an inkjet head that is provided with a common ink chamber capable of preventing significant reflection of pressure waves generated therein as ink is supplied thereto.